Since World War II ended in 1945, there have been enduring fears that World War III was just around the corner, just waiting for the unexpected spark that would trigger nuclear disaster.

It was almost exactly 100 years ago that just such a spark — the assassination of Archduke Ferdinand in Sarajevo — led directly to World War I.

Despite some close calls such as the Cuban missile crisis, World War III has so far been avoided.

However, rather than a single world war, we now appear to be witnessing multiple lesser wars that are wreaking havoc on several continents.

They are also driving dangerous wedges between Moscow and the western capitals on the one hand and between ruthlessly militant jihadists and their religious rivals, wherever they may live, on the other.

Also, the seemingly never-ending struggle between Israel and her enemies is again at a dangerous level and may yet erupt into a wide-open military conflict.

So serious are these threats to peace that the continuing horrors in various parts of Africa and in far-away Myanmar (where Bhuddists are accused of brutally persecuting Muslims) draw far less attention.

Quite naturally, it was the shocking destruction of a civilian airliner — and the almost unbearable loss of nearly 300 innocent lives — over Eastern Ukraine that has generated the most global outrage.

Definitively assessing the blame for the downing of the Malaysian jet may be extremely difficult, especially if, as has been reported (and disputed) one side or the other has managed to tamper with the evidence.

However, there appears to be an emerging consensus in western capitals that one way or another Russia’s belligerent president, Vladimir Putin, has blood on his hands. The question is: If so, what should be done about it?

It is difficult to imagine the United States and the European Union resuming normal relations with Russia, and not just because of Putin’s suspected role in arming those who, by mistake or by design, blew the airliner out of the Ukrainian sky.

Putin has suggested that the missile actually was launched by Ukrainian troops, but that seems far less plausible than the theory that the separatists, poorly trained in firing the Russian-supplied missiles, targeted the airliner by mistake.

President Barack Obama, of course, has his hands full not only with protecting America’s interests in responding to the Ukrainian crisis and the volatile situation between Israel and her neighbors, but with other hot spots that cannot be ignored.

But the president must also deal with the fact that no matter what he chooses to say or to do, he’ll inevitably draw sharp criticism. That’s a burden that goes with the occupancy of the Oval Office.

Some criticism comes, fairly enough, from those who may sincerely and respectfully disagree with him, either on a philosophical level or for more practical reasons. Such criticism is inevitable and even makes a useful contribution to the nation’s understanding of the issues.

The more aggravating criticism, however, comes from those who for purely selfish reasons see an opportunity to gain political advantage by faulting the president, often for transparently partisan reasons.

This group includes not just his political rivals but also the popular pundits who dominate certain segments of both radio and television in America.

The world is in a serious crisis. It needs intelligent, carefully calculated — and cautious — responses from the most powerful nation on this fragile globe.

What it doesn’t need is partisan grandstanding and second-guessing while the president strives to provide the leadership the world expects from the United States.